1. Field of the Invention
The present invention relates to semiconductor devices. More particularly, the invention relates to a method of generating a reference current and a current reference circuit implementing the method.
This application claims the priority of Korean Patent Application No. 10-2006-0047529, filed on May 26, 2006, the subject matter of which is hereby incorporated by reference.
2. Description of the Related Art
The performance characteristics of contemporary semiconductor devices are carefully defined in relation to a fairly narrow range of applied operating voltages and currents. The operating voltages and currents allow proper operation of the electrical circuits within semiconductor devices and must remain stable across a range of operating temperatures. One type of circuit commonly providing stable current over a range of operating conditions is referred to as a current reference circuit.
Most conventional current reference circuits generate a constant reference current irrespective of operating temperature change by compensating for a first current component proportional to absolute temperature and a second current component inversely proportional to absolute temperature. Examples of conventional reference circuits are disclosed, for example, in U.S. Pat. No. 5,990,727 and U.S. Pat. No. 6,693,332.
FIG. 1 is a diagram of an exemplary band gap reference circuit which is commonly used in conventional current reference circuits. Referring to FIG. 1, the band gap reference circuit is implemented with resistors R1 and R2 and diodes Q1-Q3 and generates a reference voltage (REF) and a corresponding reference current.
The band gap reference circuit includes a PTAT generating unit 11 generating a PTAT current component (I_PTAT) and a CTAT generating unit 13 generating a CTAT current component (I_CTAT). The PTAT generating unit 11 includes PMOS transistors P1-P3, NMOS transistors N1 and N2, a resistor R1, and bipolar transistors Q1 and Q2. The CTAT generating unit 13 includes a resistor R2 and a bipolar transistor Q3.
With this circuit configuration, a PTAT current component (I_PTAT), which is proportional to changes in temperature, flows to the PMOS transistor P3 of the PTAT generating unit 13, and a CTAT current component (I_CTAT), which is inversely proportional to the change in temperature, flows through the resistor R2 of the CTAT generating unit 13. Thus, the PTAT current component (I_PTAT) and the CTAT current component (I_CTAT) provide temperature compensation to generate the reference voltage (REF) and the corresponding reference current.
As described above, conventional current reference circuits such as the band gap reference circuit require separate circuits for generating the PTAT current component and the CTAT current component. For this reason, when conventional current reference circuits are implemented in contemporary semiconductor devices, they occupy a disproportionately large area within the device. In addition, the use of resistors within the conventional current reference circuits may lead to mismatches caused by variations in process used to fabricate the resistor, variations in the respective voltages applied to the resistors, as well as circuit local temperature variations. Such mismatches have the potential to interfere with proper operation of the conventional current reference circuit.